Field Of The Invention
The invention relates to gas lasers employing internal mirrors and more specifically to a method of mounting internal mirrors and to a gas laser having internal mirrors mounted by such method.
Background Art
U.S. Pat. No. 4,001,720 illustrates a gas laser with windows and external mirrors by way of reference. Reference is also made by way of reference to applicant's copending application Ser. No. 942, 345, filed Dec. 16, 1986, entitled "Segmented Laser Tube Structure" which illustrates an argon gas laser tube structure of a type to which the present invention may be applied.
Using an argon gas laser by way of example, the conventional method for assembling a laser tube employing windows and external mirrors generally requires the following steps:
(a) Assemble tube with windows.
(b) Connect tube to vacuum/gs source.
(c) Bake to 200.degree. C., under vacuum.
(d) Activate cathode.
(e) Fill with argon gas.
(f) Start tube and lase to determine that tube is clean; a loss of power indicates windows are dirty.
The foregoing method for installing windows to be used with external mirrors has at least these disadvantages:
(a) The presence of the glass windows inherently requires that the tube not be heated in excess of 200.degree. C. during assembly.
(b) Windows inherently get contaminated during processing and must be replaced by new windows in final assembly thus there is considerable window wastage.
(c) Contamination can exist between the windows and the mirrors.
(d) Aside from material wastage, the process is time consuming.
(e) Windows are inherently required at the tube ends.
The need for use of windows is eliminated when the laser tube is fitted with internal mirrors. This eliminates optical losses due to the windows and possible contamination between the windows and the mirrors. It is generally recognized that the use of removable and replaceable windows with external optics produces a more satisfactory tube. However, tubes with internal mirrors are generally more difficult to rework than are tubes with external mirrors. Internal mirrors are normally attached by fritting in which a solder glass is employed to join the mirror to metal on the tube body. Heating the mirror by fritting results in loss of quality, reduction in power and shifting of the coating passband. The fritting process may also stress the optical materials and may lead to deposition of frit by-products such as binders on the mirrors. Bakeout after fritting leads to a deposition on the mirrors. High temperature activation of the cathode may also lead to such deposition.
Cold welding involves installing a thin sheet of cold weld material, e.g. indium, between the surfaces to be adhered and then pressing the surfaces together with enough pressure to cause the indium to flow and form a seal. Indium provides a low vapor pressure material which is cold weldable. Laser tube mirrors have previously been secured by cold welding. However, it has not been previously known to assemble a laser tube in the manner of the present invention such that the need for windows is eliminated and the mirrors, once secured, preferably by cold welding, are free of contamination and are ready for immediate use in normal service.